U.S. patent number 11,211,020 [Application Number 16/369,319] was granted by the patent office on 2021-12-28 for high frame rate display.
This patent grant is currently assigned to Apple Inc.. The grantee listed for this patent is Apple Inc.. Invention is credited to Gihoon Choo, Hassan Edrees, Zino Lee, Chin-Wei Lin, Shinya Ono.
United States Patent |
11,211,020 |
Ono , et al. |
December 28, 2021 |
High frame rate display
Abstract
A display may have rows and columns of pixels. Gate lines may be
used to supply gate signals to rows of the pixels. Data lines may
be used to supply data signals to columns of the pixels. The data
lines may include alternating even and odd data lines. Data lines
may be organized in pairs each of which includes one of the odd
data lines and an adjacent one of the even data lines.
Demultiplexer circuitry may be configured dynamically during data
loading and pixel sensing operations. During data loading, data
from display driver circuitry may be supplied, alternately to odd
pairs of the data lines and even pairs of the data lines. During
sensing, the demultiplexer circuitry may couple a pair of the even
data lines to sensing circuitry in the display driver circuitry and
then may couple a pair of the odd data lines to the sensing
circuitry.
Inventors: |
Ono; Shinya (Cupertino, CA),
Lee; Zino (Gyeonggi, KR), Choo; Gihoon (Santa
Clara, CA), Edrees; Hassan (Cupertino, CA), Lin;
Chin-Wei (San Jose, CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
Apple Inc. |
Cupertino |
CA |
US |
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Assignee: |
Apple Inc. (Cupertino,
CA)
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Family
ID: |
1000006021697 |
Appl.
No.: |
16/369,319 |
Filed: |
March 29, 2019 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20190228726 A1 |
Jul 25, 2019 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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16120076 |
Aug 31, 2018 |
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62561583 |
Sep 21, 2017 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G09G
3/3225 (20130101); G09G 3/3266 (20130101); G09G
3/3233 (20130101); G09G 3/3648 (20130101); G09G
3/3291 (20130101); G09G 2310/0297 (20130101); G09G
2300/0819 (20130101); G09G 2300/0842 (20130101); G09G
2320/0295 (20130101); G09G 2320/0209 (20130101) |
Current International
Class: |
G09G
3/3225 (20160101); G09G 3/36 (20060101); G09G
3/3291 (20160101); G09G 3/3266 (20160101); G09G
3/3233 (20160101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
Primary Examiner: Chang; Kent W
Assistant Examiner: Bibbee; Chayce R
Attorney, Agent or Firm: Treyz Law Group, P.C. Tsai;
Jason
Parent Case Text
This application is a continuation-in-part of U.S. application Ser.
No. 16/120,076, filed Aug. 31, 2018, which is hereby incorporated
by reference herein in its entirety, and which claims the benefit
of provisional patent application No. 62/561,583, filed Sep. 21,
2017, which is hereby incorporated by reference herein in its
entirety.
Claims
What is claimed is:
1. A display, comprising: an array of display pixels arranged in
rows and columns; an odd data line that is coupled to display
pixels in odd rows within a given column of display pixels in the
array, wherein the display pixels in the odd rows within the given
column exhibit are coupled to the odd data line via a first amount
of parasitic capacitance; a first gate line coupled to display
pixels in a given one of the odd rows; an even data line that is
coupled to display pixels in even rows within the given column of
display pixels in the array, wherein the display pixels in the even
rows within the given column are coupled to the even data line via
a second amount of parasitic capacitance equal to the first amount
of parasitic capacitance, wherein the odd data line is formed on a
first side of the given column, and wherein the even data line is
formed on a second side of the given column that is different than
the first side to reduce vertical data line crosstalk; a second
gate line coupled to display pixels in a given one of the even
rows; and demultiplexer circuitry coupled to the odd and even data
lines, wherein the demultiplexer circuitry is configured to:
actively drive a first data signal onto the odd data line while
asserting the first gate line to access a selected display pixel in
the given one of the odd rows; and actively drive a second data
signal onto the even data line while asserting the second gate line
to access a selected display pixel in the given one of the even
rows.
2. The display of claim 1, wherein the odd and even data lines are
formed on opposing sides of the given column of display pixels.
3. The display of claim 1, wherein the display pixels in the odd
rows in the given column have a different orientation than the
display pixels in the even rows in the given column.
4. The display of claim 3, wherein the display pixels in the odd
rows in the given column mirrored with respect to the display
pixels in the even rows in the given column.
5. The display of claim 1, further comprising: an additional odd
data line that is coupled to display pixels in the odd rows within
an additional column of display pixels in the array; and an
additional even data line that is coupled to display pixels in the
even rows within the additional column of display pixels in the
array, wherein the demultiplexer circuitry is also coupled to the
additional odd data line and the additional even data line.
6. The display of claim 5, wherein the additional even data line is
formed closer to the even data line than the additional odd data
line.
7. The display of claim 5, wherein the additional odd data line is
formed closer to the odd data line than the additional even data
line.
8. The display of claim 5, wherein the display pixels in the given
column have a different orientation than the display pixels in the
additional column.
9. The display of claim 8, wherein the display pixels in the given
column mirrored with respect to the display pixels in the
additional column.
10. The display of claim 1, wherein the demultiplexer circuitry
comprises: a first transistor coupled between a driver circuit and
the odd data line; and a second transistor coupled between the
driver circuit and the even data line, wherein the first transistor
is configured to receive an odd selection signal, and wherein the
second transistor is configured to receive an even selection
signal.
11. A method of operating a display that includes at least one
column of pixels that is coupled to an odd data line and an even
data line, the method comprising: driving a first data signal onto
the odd data line; asserting a first gate line signal to access a
selected pixel in the column of pixels while the first data signal
is actively being driven onto the odd data line; allowing the data
line to be in a high impedance state; and while the data line is in
the high impedance state, driving a second data signal onto the
even data line, wherein a corresponding voltage change on the even
data line caused by the second data signal is not coupled to the
odd data line.
12. The method of claim 11, wherein asserting the first gate line
signal comprises loading the first data signal from the odd data
line into the selected pixel.
13. The method of claim 12, further comprising asserting a second
gate line signal to access an additional pixel in the column of
pixels.
14. The method of claim 13, wherein asserting the second gate line
signal comprises loading the second data signal from the even data
line into the additional pixel.
15. The method of claim 13, wherein the selected pixel includes a
first data loading transistor, wherein the additional pixel
includes a second data loading transistor, wherein the first data
loading transistor is separated from the odd data line by a first
distance and wherein the second data loading transistor is
separated from the even data line by a second distance that is
equal to the first distance.
16. The method of claim 11, wherein the odd and even data lines are
not immediately adjacent to each other.
17. A display comprising: a column of pixels; a first data line
that is formed on one side of the column, wherein the first data
line is coupled to pixels in odd rows of the column and wherein the
pixels in the odd rows of the column exhibit a first amount of
parasitic capacitance to the first data line; a first scan line
coupled to a first pixel in the column of pixels, wherein the first
scan line is asserted to access the first pixel while a first data
signal is actively being driven onto the first data line; a second
data line that is formed on another side of the column, wherein the
second data line is coupled to pixels in even rows of the column
and wherein the pixels in the even rows of the column exhibit a
second amount of parasitic capacitance to the second data line that
is equal to the first amount of parasitic capacitance; and a second
scan line coupled to a second pixel in the column of pixels,
wherein the second scan line is asserted to access the second pixel
while a second data signal is actively being driven on the second
data line.
18. The display of claim 17, wherein the pixels in the odd rows
have a different orientation than the pixels in the even rows.
19. The display of claim 17, wherein only one of the first and
second data lines is actively driven at any point in time during
operation of the display.
Description
BACKGROUND
This relates generally to electronic devices, and, more
particularly, to electronic devices with displays.
Electronic devices such as cellular telephones, computers, and
other electronic devices often contain displays. A display includes
an array of pixels for displaying images. Display driver circuitry
such as data line driver circuitry may supply data signals to the
pixels. Gate line driver circuitry in the display driver circuitry
can be used to provide control signals to the pixels.
It can be challenging to provide display driver circuitry for a
display. If care is not taken, frame rates will be too low or
display performance will otherwise not be satisfactory.
SUMMARY
A display may have rows and columns of pixels. Gate lines may be
used to supply gate line signals to rows of the pixels. Data lines
may be used to supply data signals to columns of the pixels. The
data lines may include alternating even and odd data lines. Data
lines may be organized in pairs each of which includes one of the
odd data lines and an adjacent one of the even data lines. Columns
of pixels with mirrored layouts may flank each pair of data
lines.
Demultiplexer circuitry may be configured dynamically during data
loading and pixel sensing operations. During data loading, data
from display driver circuitry may be supplied, alternately, to odd
pairs of the data lines and even pairs of the data lines. During
sensing, the demultiplexer circuitry may couple a pair of the even
data lines to sensing circuitry in the display driver circuitry and
then may couple a pair of the odd data lines to the sensing
circuitry.
Configurations in which pixels in alternating rows are coupled
alternately to the odd and even data lines and configurations in
which rows of pixels each include multiple gate lines may also be
used. Configurations for reducing vertical column crosstalk and for
reducing the difference in parasitic capacitance between odd and
evens rows are also provided.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of an illustrative electronic device
having a display in accordance with an embodiment.
FIG. 2 is a top view of an illustrative display in an electronic
device in accordance with an embodiment.
FIG. 3 is a circuit diagram of illustrative multiplexer and pixel
circuitry in a display in accordance with an embodiment.
FIG. 4 is a timing diagram of illustrative control signals in a
display in accordance with an embodiment.
FIG. 5 is an illustrative pixel circuit in a display in accordance
with an embodiment.
FIG. 6 is a flow chart of illustrative operations associated with
operating a display in accordance with an embodiment.
FIG. 7 is a top view of a portion of a display with power supply
lines, data lines, and control lines in accordance with an
embodiment.
FIG. 8 is a cross-sectional side view of an illustrative display in
accordance with an embodiment.
FIG. 9 is a diagram showing how display demultiplexer circuitry may
be operated during data loading in accordance with an
embodiment.
FIG. 10 is a diagram showing how display demultiplexer circuitry
may be operated during current sensing operations in accordance
with an embodiment.
FIG. 11 is a timing diagram of illustrative data loading control
signals for two successive frames in accordance with an
embodiment.
FIG. 12 is a diagram corresponding to pixel loading patterns in
successive frames using the signals of FIG. 11 in accordance with
an embodiment.
FIG. 13 is a timing diagram of additional illustrative data loading
control signals for two successive frames in accordance with an
embodiment.
FIG. 14 is a diagram corresponding to pixel loading patterns in
successive frames using the signals of FIG. 13 in accordance with
an embodiment.
FIG. 15 is a timing diagram of illustrative current sensing control
signals for two successive frames in accordance with an
embodiment.
FIG. 16 is a diagram corresponding to pixels being sensed during
the successive frames of FIG. 15 in accordance with an
embodiment.
FIG. 17 is a diagram of illustrative pixels in a display in
accordance with an embodiment.
FIG. 18 is a timing diagram of illustrative control signals for
operating the circuitry of FIG. 17 in accordance with an
embodiment.
FIGS. 19, 20, and 21 illustrate data loading operations in
accordance with embodiments.
FIG. 22 is a diagram showing how an array of display pixels can be
affected by vertical crosstalk and a difference in row-to-row
parasitic capacitance.
FIG. 23 is a timing diagram illustrating how vertical crosstalk
between odd and even rows can affect data accuracy.
FIG. 24 is a diagram showing how the odd and even data lines may be
interlaced to help mitigate the difference in row-to-row parasitic
capacitance in accordance with an embodiment.
FIG. 25 is a diagram showing an illustrative array of display
pixels where vertical crosstalk and any difference in row-to-row
parasitic capacitance are minimized in accordance with an
embodiment.
FIG. 26 is a timing diagram showing illustrative waveforms
associated with the operation of the display pixel array shown in
FIG. 25 in accordance with an embodiment.
DETAILED DESCRIPTION
An illustrative electronic device of the type that may be provided
with a display is shown in FIG. 1. Electronic device 10 of FIG. 1
may be a tablet computer, laptop computer, a desktop computer, a
monitor that includes an embedded computer, a monitor that does not
include an embedded computer, a display for use with a computer or
other equipment that is external to the display, a cellular
telephone, a media player, a wristwatch device or other wearable
electronic equipment, or other suitable electronic device.
As shown in FIG. 1, electronic device 10 may have control circuitry
16. Control circuitry 16 may include storage and processing
circuitry for supporting the operation of device 10. The storage
and processing circuitry may include storage such as hard disk
drive storage, nonvolatile memory (e.g., flash memory or other
electrically-programmable-read-only memory configured to form a
solid state drive), volatile memory (e.g., static or dynamic
random-access-memory), etc. Processing circuitry in control
circuitry 16 may be used to control the operation of device 10. The
processing circuitry may be based on one or more microprocessors,
microcontrollers, digital signal processors, baseband processors,
power management units, audio chips, application specific
integrated circuits, etc.
Input-output circuitry in device 10 such as input-output devices 12
may be used to allow data to be supplied to device 10 and to allow
data to be provided from device 10 to external devices.
Input-output devices 12 may include buttons, joysticks, scrolling
wheels, touch pads, key pads, keyboards, microphones, speakers,
tone generators, vibrators, cameras, sensors, light-emitting diodes
and other status indicators, data ports, etc. A user can control
the operation of device 10 by supplying commands through
input-output devices 12 and may receive status information and
other output from device 10 using the output resources of
input-output devices 12.
Input-output devices 12 may include one or more displays such as
display 14. Display 14 may be a touch screen display that includes
a touch sensor for gathering touch input from a user or display 14
may be insensitive to touch. A touch sensor for display 14 may be
based on an array of capacitive touch sensor electrodes, acoustic
touch sensor structures, resistive touch components, force-based
touch sensor structures, a light-based touch sensor, or other
suitable touch sensor arrangements.
Control circuitry 16 may be used to run software on device 10 such
as operating system code and applications. During operation of
device 10, the software running on control circuitry 16 may display
images on display 14 using an array of pixels in display 14.
Display 14 may have a rectangular shape (i.e., display 14 may have
a rectangular footprint and a rectangular peripheral edge that runs
around the rectangular footprint) or may have other suitable
shapes. Display 14 may be planar or may have a curved profile.
Display 14 may be an organic light-emitting diode display or other
suitable type of display.
A top view of a portion of display 14 is shown in FIG. 2. As shown
in FIG. 2, display 14 may have an array of pixels 22 formed from
substrate structures such as substrate 36. Substrates such as
substrate 36 may be formed from glass, metal, plastic, ceramic, or
other substrate materials. Pixels 22 may receive data signals over
signal paths such as data lines D and may receive one or more
control signals over control signal paths such as gate lines G
(sometimes referred to as control lines, scan lines, emission
enable control lines, gate signal paths, etc.). There may be any
suitable number of rows and columns of pixels 22 in display 14
(e.g., tens or more, hundreds or more, or thousands or more).
Pixels 22 may have different colors (e.g., red, green, and blue) to
provide display 14 with the ability to display color images. Pixels
22 may contain respective light-emitting diodes and pixel circuits
that control the application of current to the light-emitting
diodes. The pixel circuits in pixels 22 may contain transistors
(e.g., thin-film transistors on substrate 36) having gates that are
controlled by gate line signals on gate lines G.
Display driver circuitry 20 may be used to control the operation of
pixels 22. Display driver circuitry 20 may be formed from
integrated circuits, thin-film transistor circuits, or other
suitable circuitry. Thin-film transistor circuitry for display
driver circuitry 20 and pixels 22 may be formed from polysilicon
thin-film transistors, semiconducting-oxide thin-film transistors
such as indium gallium zinc oxide transistors, or thin-film
transistors formed from other semiconductors.
Display driver circuitry 20 may include display driver circuits
such as display driver circuitry 20A and gate driver circuitry 20B.
Display driver circuitry 20A may include a display driver circuit
20A-1 that is formed from one or more display driver integrated
circuits (e.g., timing controller integrated circuits) and/or
thin-film transistor circuitry and may include demultiplexer
circuitry 20A-2 (e.g., a demultiplexer formed from thin-film
transistor circuitry or formed in an integrated circuit). Gate
driver circuitry 20B may be formed from gate driver integrated
circuits or may be formed from thin-film transistor circuitry.
Display driver circuitry 20A may contain communications circuitry
for communicating with system control circuitry such as control
circuitry 16 of FIG. 1 over path 32. Path 32 may be formed from
traces on a flexible printed circuit or other conductive lines.
During operation, the control circuitry (e.g., control circuitry 16
of FIG. 1) may supply circuitry 20A with information on images to
be displayed on display 14.
To display images on display pixels 22, display driver circuitry
20A may supply image data to data lines D while issuing control
signals (e.g., clock signals, a gate start pulse, etc.) to
supporting display driver circuitry such as gate driver circuitry
20B over path 38. Circuitry 20A may also dynamically adjust
demultiplexer circuitry 20A-2 by supplying clock signals (select
signals) and other control signals to demultiplexer circuitry
20A-2.
In some configurations for display 14, each column of pixels 22 may
include multiple data lines (e.g., at least two, at least three,
etc.). An illustrative configuration for display 14 in which each
column of pixels 22 include a pair of data lines D is shown in FIG.
3. A gate line may be associated with each row of pixels 22. Nodes
N show where data lines D are coupled to the pixel circuits of
pixels 22. Along each column, pixels are alternately coupled to odd
and even data lines in each pair of data lines. As shown in FIG. 3,
demultiplexer circuitry 20A-2 may contain switches SW that are
controlled using control signals CLK1 and CLK2. FIG. 4 is a timing
diagram showing signals that may be used in controlling display 14
of FIG. 3.
In high frame rate configurations for display 14, the row time
("1H" of FIG. 4) associated with controlling rows of pixels 22
tends to decrease. This can make it difficult to complete desired
control operations (e.g., to load data into each row of pixels 22).
By using multiple data lines per column of pixels 22, the control
signals (e.g., the gate signals of FIG. 4) in successive rows can
be staggered and can overlap in time, allowing each gate signal to
be asserted for more than one row time (e.g., more than 1H).
Consider, as an example, the loading of pixel 22-1 in row n-1 of
FIG. 3 and the loading of pixel 22-2 in row n of FIG. 3. As shown
in FIG. 4, gate signal gate(n-1) is taken low at time t1. Pixel
22-1 can then be loaded via data line D1. Loading can start during
time period TP1 and can finish during time period TP2. At time t2,
before the signal gate(n-1) is deasserted at time t3, gate signal
gate(n) is asserted in row n. This allows pixel 22-2 to be loaded
by data line D2. It is not necessary for gate signal gate(n-1) to
complete before gate signal gate(n) is asserted, because pixel 22-1
is not coupled to data lines D2 (pixel 22-1 is coupled to data line
D1 by a node N, but no nodes N couple pixel 22-1 to data line D2).
As shown in FIG. 4, each gate signal may have a pulse width that is
greater than the pulse widths of clocks CLK1 and CLK2.
Any suitable pixel circuit may be used for forming pixels 22 in
display 14. An illustrative pixel circuit is shown in FIG. 5. Other
pixel circuitry may be used, if desired.
In the illustrative configuration of FIG. 5, pixel circuit 40 has
switching transistors T1 and T2, drive transistor TD, and emission
enable transistor TE. Transistors T1 and T2 are controlled by gate
signals from gate driver circuitry 20B while data is provided via
data line D. Storage capacitor Cst is used to retain data on node
ND during emission operations. Reference voltage line Vref may be
used in supplying a reference voltage Vref to pixel circuit 40.
During sensing operations (for threshold voltage compensation
measurements), data line D may be used to sense the current
associated with the pixel. Drive transistor TD and enable
transistor TE are coupled in series between positive power supply
terminal Vddel and negative (ground) power supply terminal Vssel.
When transistor TE is on, emission is enabled and the amount of
light 42 that is emitted from light-emitting diode 48 is determined
by the current flowing through transistor TD. This current is
determined based on the magnitude of the signal on node ND, which
is coupled to the gate of transistor TD.
A flow chart of illustrative operations involved in displaying an
image frame using pixels 22 (e.g., pixels 22 with pixel circuit 40
of FIG. 5) is shown in FIG. 6. During the operations of block 50,
transistors T1 and T2 are turned on and reference data Vdata-ref is
loaded onto node ND. During the operations of block 52, sensors
(e.g., current sensors) in circuitry 20A are used to sense pixel
currents via data lines D. During pixel sensing operations,
transistor T2 is turned off, transistor TE is turned on. Transistor
T1 is on and allows the pixel current to flow through transistors
TE and T1 to data line D for sensing. The sensed current is
indicative of the threshold voltage of transistor TD. Following the
sensing operations of block 52, a frame of corresponding pixel
compensation values (e.g., digital values) can be produced by
circuitry 20A. This frame of compensation data can be used to
compensate an image frame for threshold voltage variations among
pixels 22. The image frame (e.g., an image frame of data values for
each pixel that have been compensated with the compensation data in
the frame of compensation data) can be loaded into pixels 22 during
the operations of block 54. During the operations of block 54,
transistors T1 and T2 may be turned on for data loading while
transistor TE is turned off. Compensated data is loaded into each
pixel using data lines D. During the operations of block 56,
transistors T1 and T2 are off and transistor TE is on to enable
current to flow through light-emitting diode 44. The amount of
current that flows through diode 44 and therefore the amount of
light 42 that is emitted by diode 44 is determined by the current
flowing through drive transistor TD, which is determined by the
data on node ND.
FIG. 7 is a top view of a portion of display 14 showing an
illustrative layout for power supply lines Vssel and Vddel and for
reference line 46 and data lines DATA (sometimes referred to as
data lines D). The illustrative layout of FIG. 8 allows each
reference line 46 to be shared between an adjacent even column of
pixels 22 and odd column of pixels 22 and allows each power supply
line Vssel and each power supply line Vddel to be shared between
adjacent even and odd columns of pixels 22. The layout of each
pixel circuit 40 in each even column may have mirror symmetry with
the layout of each pixel circuit 40 in an adjacent odd column. Data
lines DATA may extend vertically through pixels 22 in pairs. Each
pair of data lines may include a first data line for loading data
into an odd column of pixels 22 and a second data line for loading
data into an even column of pixels 22.
A cross-sectional side view of display 14 of FIG. 14 is shown in
FIG. 8. As shown in FIG. 8, dielectric layer 62 may be formed on
lower thin-film transistor circuitry layers, a substrate layer
and/or other layers (see, e.g., layer 60). Power supply lines Vddel
and reference lines 46 may be formed on layer 62. Planarization
layer 64 may cover these lines and layer 62. Power supply lines
Vssel and data lines D (e.g., data lines running parallel to each
other in pairs) may be formed on layer 64.
In configurations for display 14 with mirror symmetry pixel layouts
and pairs of data lines of the type shown in FIGS. 7 and 8, the
space consumed by signal lines can be reduced by consolidating
signal lines such as the power supply lines and reference voltage
lines. However, parasitic capacitances between adjacent data lines
D in each pair of data lines may arise (see, e.g., parasitic
capacitances Cp of FIG. 9). If care is not taken (e.g., if odd and
even columns of pixels are loaded separately), there is a potential
for capacitive coupling between the even column data lines and the
odd column data lines to adversely affect the accuracy of loaded
data.
To address this concern, data can be driven onto the data lines of
each pair of data lines simultaneously. Demultiplexing circuitry
20A-2 may be used to reduce fanout between circuit 20A-1 and data
lines D. To accommodate the use of demultiplexing circuitry 20A-2
in a configuration for display 14 with pairs of simultaneously
driven data lines, demultiplexing circuitry 20A-2 can alternate
between a first state in which odd pairs of columns are loaded and
a second state in which even pairs of columns are loaded.
This type of arrangement is shown in FIG. 9. As shown in FIG. 9,
demultiplexing circuitry 20A-2 may be dynamically configured in
accordance with control signals (sometimes referred to as clock
signals CLK1 and CLK2) such as SEL_A and SEL_B. When SEL_A is taken
low, data is loaded from demultiplexer circuitry 20A-2 into odd
pairs of columns and when SEL_B is taken low data is loaded into
even pairs of columns. For example, when SEL_A is taken low, data
is located into pixels 22A and 22B of each odd column pair using
data lines D(ODD PAIR) and when SEL_B is taken low, data is located
into pixels 22C and 22D of each even column pair using data lines
D(EVEN PAIR). The alternating column pair loading pattern used in
FIG. 9, which may be used during the operations of blocks 50 and 54
of FIG. 6, may help enhance data loading accuracy.
As shown in FIG. 10, pixel sensing (e.g., sensing operations to
measure currents for threshold voltage compensation during the
operations of block 52 of FIG. 6), may use a different pattern of
data lines. In particular, during sensing operations, demultiplexer
circuitry 20A may be configured to alternate between a first state
in which first and second odd data lines D_O from first and second
adjacent column pairs (e.g., ODD PAIR and EVEN PAIR) are used to
provide current measurements to circuitry 20A-1 and a second state
in which first and second even data lines D_E from the first and
second adjacent columns pairs are switched into use for current
sensing. Differential current sensing may be used to mitigate the
impact of potential fabrication variations (e.g., variations that
might make the capacitive coupling different between a gate line G
and a first data line relative to the capacitive coupling between
that gate line and a second data line that is paired with the first
data line). The use of differential sensing may help remove common
mode noise from horizontal lines such as gate lines G that overlap
the data lines.
The patterns used for loading and sensing may, if desired, vary
between frames. As shown in the timing diagram of FIG. 11 and the
corresponding pixel loading patterns for frames m and m+1 in FIG.
12, for example, the column pairs that are loaded may vary between
frames. In frame m, odd column pairs may be loaded. In frame m+1,
even column pairs may be loaded. This alternating pattern can help
reduce artifacts from capacitive coupling between adjacent pairs of
columns (and associated adjacent pairs of data lines). FIGS. 13 and
14 show an arrangement in which both column pair and row
alternations are used (e.g., to form an alternating checkerboard
pattern of loaded sets of pixels between respective frames). Other
time varying patterns may be used, if desired.
An illustrative arrangement for varying the pattern of data lines
used during sensing between successive frames is shown in the
timing diagram of FIG. 15 and the corresponding pixel and data line
diagrams for frames m and m+1 in FIG. 16. As shown in FIGS. 15 and
16, in the mth frame, odd data lines D_O (e.g., pairs of lines for
differential sensing) may be switched into use before switching
even data lines D_E into use. In the m+1.sup.st frame, this pattern
is reversed and even data lines D_E are used before odd data lines
D_O.
An alternative configuration for loading pixels 22 is shown in the
pixel diagram of FIG. 17 and the corresponding timing diagram of
FIG. 18. In this arrangement, each row of pixels 22 shares two gate
lines (or sets of gate lines) such as odd gate lines G_O and even
gate lines G_E. When CLK1 is asserted (e.g., taken low), odd pairs
of columns are selected by demultiplexer circuitry 20A-2. When CLK2
is asserted (e.g., taken low), even pairs of columns are selected.
Gate signals on odd lines G_O are asserted and deasserted in
accordance with the falling edges of CLK1 and CLK2, respectively.
Gate signals on even lines G_E are asserted and deasserted in
accordance with the falling edges of CLK2 and CLK1, respectively.
During the period of time in which each pair of data lines is
loaded with data, first the odd gate line and then the even gate
line is asserted, thereby loading the left-hand pixel 22 and then
the right-hand pixel associated with that pair of data lines.
FIGS. 19, 20, and 22 show additional illustrative arrangements for
loading pixels 22 in display 14. In the configuration of FIG. 19, a
gate line G in a given row is asserted while (in a first
demultiplexer state) odd date lines D_O are used in providing data
to a first row of pixels 22' that are associated with the asserted
gate line G and (in a second demultiplexer state) even data lines
D_E are used in providing data to a second row of pixels 22'' that
are associated with the asserted gate line G.
FIG. 20 shows an illustrative configuration in which (1) odd date
lines D_O are provided with data and are then left floating, (2)
even data lines D_E are provided with data and are then left
floating, and (3) gate control signal SC is asserted on a gate line
G to load data from the odd data lines into a first row of pixels
22' associated with the gate line and to load data from the even
data lines into a second row of pixels 22'' associated with the
gate line.
FIG. 21 shows an illustrative configuration in which demultiplexer
20A-2 uses 1:2 demultiplexer circuits. Demultiplexer 20A-2 first
provides odd data lines D_O with data while both the odd and even
lines are coupled to the input of each 1:2 demultiplexer. After
switching the state of demultiplexer 20A-2, data is provided to
even data lines D_E. After loading the odd and even data lines with
data in this way, the pixels are loaded (programmed). During
programing, gate line G supplies signal SC (signal SC is taken low)
and a first row of pixels 22' associated with the gate line G is
loaded with data from the odd data lines D_O while a second row of
pixels 22'' is loaded with data from the even data lines D_E.
The use of odd and even data lines in each column of display pixels
may give rise to vertical column crosstalk between the odd and even
data lines (see FIG. 22). As shown in FIG. 22, a first row (i.e.,
odd row "2m+1") includes a row of pixels 22 each having a p-type
data loading transistor 100 having a source-drain terminal
connected to the odd data line D_odd and a gate terminal that
receives gate line signal G_odd(2m+1). Data loading transistor 100
is similar to transistor T1 in the exemplary pixel structure of
FIG. 5, which is used to load in a data signal during the data
programming phase. Similarly, a second row (i.e., even row "2m+2")
includes a row of pixels 22 each having a p-type data loading
transistor 100 having a source-drain terminal connected to the even
data line D_even and a gate terminal that receives gate line signal
G_even(2m+2). The gate line signals are sometimes referred to as
"scan" signals. Other rows within display 14 may be formed in this
alternating fashion in which the odd rows are connected to the odd
data lines D_odd and the even rows are connected to the even data
lines D_even. All pixels 22 in the arrangement of FIG. 22 are
formed in the same orientation, as indicated by the imaginary
notation "F" at the corner of each pixel 22.
The odd data lines receive corresponding data signals through
p-type selection transistor 120 within demultiplexer 20A-2, whereas
the even data lines receives corresponding data signals through
p-type selection transistor 122 within demultiplexer 20A-2.
Transistors 120 receive a selection control signal SEL_odd, which
is driven low to pass data signal Data(n) in the first column to
data line D_odd(n) and to pass data signal Data(n+1) in the second
column to data line D_odd(n+1). Similarly, transistors 122 receive
a selection control signal SEL_even, which is driven low to pass
data signal Data(n) in the first column to data line D_even(n) and
to pass data signal Data(n+1) in the second column to data line
D_even(n+1).
One potential problem with the display configuration of FIG. 22 is
that due to the formation of the odd and even data lines right next
to each other, a relatively large parasitic coupling capacitance
102 exists between each pair of adjacent data lines D_odd and
D_even. A large parasitic coupling capacitance 102 may induce
vertical data line crosstalk, which can degrade the accuracy of
data signals being loaded into the pixel array. This undesired
effect is shown in the timing diagram of FIG. 23. At time t1,
signal SEL_odd is driven low to pass display driver circuit ("DIC")
data for row "2m+1" onto corresponding data lines D_odd. At time
t2, gate line signal G_odd(2m+1) is driven low to turn on data
loading transistors 100 to pass the data signals from the odd data
lines onto row "2m+1".
At time t3, signal SEL_odd is driven high, which allows data lines
D_odd to float. Thus, between time t2 and t3, data lines D_odd are
actively driven, but data lines D_odd will be in a high impedance
state after SEL_odd is driven high. At time t4, signal SEL_even is
driven low to pass display driver circuit data for row "2m+2" onto
corresponding data lines D_even. When the voltage on D_even changes
at this point, the large parasitic data line capacitance 102 will
cause any voltage perturbation on D_even to be coupled onto D_odd,
as shown by arrow 190, especially since D_odd is in high impedance
state during this time. Since the data loading transistors in row
"2m+1" is still on, data kicking in this way can negatively impact
data driving accuracy. At time t5, gate line signal G_odd(2m+2) is
driven low to turn on data loading transistors 100 to pass the data
signals from the even data lines onto row "2m+2". At time t6, gate
line signal G_odd(2m+1) is driven high to turn off the data loading
transistors 100. The vertical crosstalk may cause data kicking in
every clock cycle whenever new data is first driven onto data line
D_odd while D_even is floating or vice versa.
The pixel configuration of FIG. 22 can also suffer from another
problem where odd and even rows have different parasitic
capacitances to the corresponding data lines. As shown in FIG. 22,
pixels 22 in the first row have internal nodes that are coupled to
data line D_odd via parasitic capacitance 110, whereas pixels 22 in
the second row have internal nodes that are coupled to data line
D_even via parasitic capacitance 112. Because D_even is farther
from the pixel than D_even as shown in the example of FIG. 22,
parasitic capacitance 110 will be necessarily different than
parasitic capacitance 112. This difference in parasitic capacitance
between rows can result in content-dependent non-uniformity between
rows, another undesired effect.
In accordance with an embodiment, FIG. 24 is a diagram showing how
the odd and even data lines may be intertwined to help mitigate the
difference in row-to-row parasitic capacitance. As shown in FIG.
24, data lines D_odd and D_even are braided and alternate position
between successive rows (as shown by crossover region 130), which
allow data line D_odd to be closer to the pixels 22 in the odd rows
"2m+1" and "2m+3" and allow data line D_even to be closer to the
pixels 22 in even rows "2m+2" and "2m+4". Arranged in this way,
pixels 22 in the odd rows have internal nodes that are coupled to
data line D_odd via parasitic capacitance 110, and pixels 22 in the
even rows have internal nodes that are coupled to data line D_even
via parasitic capacitance 110', which is identical to that of
parasitic capacitance 110. Because parasitic capacitance 110 is
substantially equivalent to parasitic capacitance 110', any
row-to-row difference is eliminated, thereby solving the
content-dependent non-uniformity problem between odd and even
rows.
FIG. 25 is a diagram showing an illustrative array of display
pixels where vertical crosstalk and any difference in row-to-row
parasitic capacitance are both minimized in accordance with an
embodiment. As shown in FIG. 25, a first row (e.g., odd row "2m+1")
may include a row of pixels 22 each having a p-type data loading
transistor 200 having a source-drain terminal coupled to the odd
data line D_odd and a gate terminal that receives gate line signal
G_odd(2m+1). Note that data line D_odd is formed to the left of
pixel 22. Transistor 200 may be similar to transistor T1 in the
exemplary pixel structure of FIG. 5 or can generally represent any
data loading transistor configured to load data signals during the
data programming phase.
In contrast, a second row (i.e., even row "2m+2") may include a row
of pixels 22 each having a p-type data loading transistor 200
having a source-drain terminal coupled to the even data line D_even
and a gate terminal that receives gate line signal G_even(2m+2).
Note that data line D_even is formed to the right of pixel 22. The
gate line signals are sometimes referred to as scan signals, scan
line signals, scan control signals, row control signals, etc. Other
rows within display 14 may be formed in this alternating fashion in
which the odd rows are connected to the odd data lines D_odd formed
on one side of the pixel, whereas the even rows are connected to
the even data lines D_even formed on the other side of the
pixel.
The odd data lines may receive corresponding data signals from a
first data driver circuit through p-type selection transistor 220
within demultiplexer 20A-2, whereas the even data lines may receive
corresponding data signals from a second data driver circuit
through p-type selection transistor 222 within demultiplexer 20A-2.
Transistors 220 may receive a selection control signal SEL_odd,
which is asserted (e.g., driven low) to pass data signal Data(n)
from the first data driver circuit in the first column to data line
D_odd(n) and to pass data signal Data(n+1) from the second data
driver circuit in the second column to data line D_odd(n+1).
Similarly, transistors 222 may receive a selection control signal
SEL_even, which can be asserted (e.g., driven low) to pass data
signal Data(n) in the first column to data line D_even(n) and to
pass data signal Data(n+1) in the second column to data line
D_even(n+1).
In contrast to the arrangement of FIG. 22, pixels 22 in the example
of FIG. 25 are not all formed in the same orientation. As shown by
the imaginary notation "F" at the corner of each pixel 22, the
pixels in different rows are vertically mirrored with respect to
each other. This presents a more efficient layout because data
loading transistor 200 is coupled to data line D_odd to the left in
the odd rows, whereas data loading transistor 200 is coupled to
data line D_even to the right in the even rows. This example in
which the odd data lines are formed to the left and the even data
lines are formed to the right of each pixel is merely illustrative.
If desired, the odd data liens maybe formed to the right while the
even data liens are formed to the left of each pixel. Moreover,
adjacent columns may also be mirrored with respect to one another.
Mirrored in this way, the even data lines from adjacent columns
will be placed next to one another (e.g., data line D_even(n) is
placed next to data line D_even(n+1), etc.). The rest of the array
may be formed by replicating the two columns shown in FIG. 25.
Configured in this way, the odd and even data lines of each column
are placed far from any other data line that can potentially impact
the data loading accuracy. By placing data lines D_odd and D_even
on either side of pixel 22, the parasitic capacitance 202 even the
odd and even data line pair is much lower than that of capacitance
102 (see FIG. 22) and thus vertical cross is substantially
mitigated. The fact that the even data lines between adjacent
columns or that the odd data lines between adjacent columns are
placed next to each other is not an issue since they will both be
actively addressed at the same time, which circumvents the high
impedance scenario previous discussed.
Still referring to FIG. 25, pixels 22 in the odd rows have internal
nodes that are coupled to data line D_odd via parasitic capacitance
210, whereas pixels 22 in the even rows have internal nodes that
are coupled to data line D_even via parasitic capacitance 212.
Because the pixels from row-to-row are mirrored, the distance
between the internal nodes and the corresponding data lines should
be equidistant. Thus, parasitic capacitance 210 should be identical
to parasitic capacitance 212, thereby minimizing any row-to-row
difference is eliminated and solving the content-dependent
non-uniformity problem between odd and even rows.
FIG. 26 is a timing diagram showing illustrative waveforms
associated with the operation of the display pixel array shown in
FIG. 25 in accordance with an embodiment. At time t1, signal
SEL_odd may be asserted to pass display driver integrated circuit
("DIC") data for row "2m+1" onto corresponding odd data lines
D_odd. At time t2, gate line signal G_odd(2m+1) is driven low to
turn on data loading transistors 200 to pass the data signals from
the odd data lines onto row "2m+1".
At time t3, signal SEL_odd may be deasserted (e.g., driven high),
which allows data lines D_odd to float. Thus, between time t2 and
t3, data lines D_odd are actively driven by the data line drivers,
but data lines D_odd will be in a high impedance state after
SEL_odd is deasserted. At time t4, signal SEL_even may be asserted
to pass DIC data for row "2m+2" onto corresponding data lines
D_even. When the voltage on D_even changes at this point, there
will be no data kicking to D_odd since parasitic capacitance 202 is
low. At time t5, gate line signal G_odd(2m+2) is asserted to turn
on data loading transistors 200 to pass the data signals from the
even data lines onto row "2m+2". At time t6, gate line signal
G_odd(2m+1) is driven high to turn off the corresponding data
loading transistors 200. In contrast to the example of FIG. 23, the
operation shown in FIG. 26 experiences no vertical crosstalk.
The foregoing is merely illustrative and various modifications can
be made to the described embodiments. The foregoing embodiments may
be implemented individually or in any combination.
* * * * *